It is understood in this document that a transition metal is a metal whose layer d is partially filled with the normal oxidation number of this metal. This concerns elements filling the periods III to XII of the periodic table of elements with eighteen columns.
For example, these metals may be Tc, Ru, Co, Pt, Fe, Os, Ir, W, Re, Cr, Mo, Mn, Ni, Rh, Pd, Nb and Ta.
Technetium nitruro complexes have been described by J. Baldas and al. in the following documents : international patent application WO-85/03 063 and the book entitled "Technetium in Chemistry and Nuclear Medicine" Ed. M. Nicolini, G. Bandoll, U. Mazzi, Cortine Int. Verone, 1986, pages 103 to 108.
In these documents, the preparation of technetium nitruro complexes is described via the substitution reaction on TcNCl.sub.4 and it is specified that these complexes may be used as radiopharmaceutical products, but these documents provide no conclusive result concerning the fixation of these complexes in the human body and thus give no indication as to their tropisms in relation to certain organs, especially the brain. Moreover, the ligands tested are mainly diethylenetriaminepentacetate (DTPA), methylene disphosphonate (MDP), cysteine (CYS), gluconate (GLUC), ethane-1-hydroxy-1,1-disphosphonate (EHDP), N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetate (HIDA), N-(2,6-diisopropylphenylcarbamoylmethly)iminodiacetate (PIPIDA) and dimercaptosuccinate (DMSA).
Radiopharmaceutical products able to be used for the optical image formation of the brain need to possess certain characteristics which first of all are to be able to traverse the hematoencephalic barrier and be fixed and accumulated in the brain within a relatively short period of time at a high concentration and to remain there for a sufficient period so that an examination can be made.
Technetium neutral complexes possessing these characteristics are described in the documents EP-A- 0 394 126, EP-A 163 119, EP-A- 0 279 417, EP-A 0 194 843 and FR-A- 2 651 232.
In the documents EP-A- 194 843, EP-A- 163 119, FR-A 2 651 232 and EP-A- 0 394 126, the complexes used include ligands with amino ceto or thiol groups, which may be coupled to a radioactive metallic ion, such as TcO. These documents do not deal with technetium nitruro complexes.
However, the document EP-A 0 279 417 does refer to diaminodithiols ligands with ester substituents which may be coupled to a pattern Tc.tbd.N so as to form nitruro complexes able to be used for forming an optical image of the brain.
The document WO-90/06137 also describes transition metal nitruro complexes able to be used as a cardiac tropism radiopharmaceutical product, but the biodistribution results obtained with the complexes of the examples of this document show that they are scarcely retained by the brain.
However, following research conducted on other radiopharmaceutical products of the same type, some of them have been found to possess satisfactory properties enabling them to be used as diagnostic or therapy products having a cerebral tropism for, for example, the use of a scintiscanner examining the brain.